Many food products containing and including edible fats and oils, i.e., fats and oils of animal and vegetable origin or modified fats and oils of animal and vegetable origin, become rancid or have an undesirable taste and/or color imparted thereto during storage, especially upon exposure to or on contact with oxygen. A number of chemical compounds have been employed for avoiding or reducing these effects so that food products containing fats or oils may be kept for longer periods of time, but such agents have not been entirely satisfactory or effective in many cases. Furthermore, such chemical compounds are usually synthetic chemical products not derived from or identical with material of natural food classifications and, as a consequence, there has been some question as to the advisability of using such compounds in food compositions.
Principal antioxidants of the above kinds heretofore employed included BHA (butylated hydroxyanisole), BHT (butylated hydroxytoluene) and TBHQ (tertiary butylhydroquinone), as well as some other chemicals of which one example is propyl gallate (PG). While these materials have been quite effective in animal fats, such as lard, they are much less useful in some other applications. Their volatility and tendency to decompose at high temperatures makes them not entirely suitable for deep fat fried foods. Indeed, their usefulness for stability of vegetable oils is less than satisfactory. For example, they are not entirely effective in protecting against off-flavor development, such as the so-called reversion flavor, that occurs, with passage of time, in soybean oil. For these and other reasons, there has been a need for improvement in the field of antioxidants, especially those to be used with food materials that comprise or consist of fats or oils.
It has been heretofore known that antioxidant properties are possessed by tempeh, a fermented soybean product obtained by fermenting soybeans with a fungus, either Rhizopus oligosporus or Rhizopus oryzae. Food products containing tempeh, such as fish or fatty meat products exhibit improved stability, see U.S. Pat. No. 3,681,085 (1972). Further, it has heretofore been found that by extracting tempeh with a mixture of hexane and methanol, a component of tempeh, namely oil of tempeh, can be recovered, see U.S. Pat. No. 3,762,933 (1973) and 3,885,256 (1974), which exhibits enhanced antioxidant properties relative to those of tempeh. This oil of tempeh has been found to be useful in stabilizing a wide variety of edible oils and fats.